Such lighting devices include a light source and, disposed thereafter, an optical element having a decoupling surface for the light emitted by the light source. For example, the light source can be a semiconductor chip, with a suitably shaped potting compound as the optical element.
For the light emitted by the light source to be decoupled as effectively as possible, the optical element must be adapted to the light source.
With special light sources, particularly coherent light sources such as semiconductor lasers, for example, which have a comparatively well-defined and highly directed radiation characteristic, it is often possible to use prefabricated optical elements/element shapes that have been optimized for this class of light sources, such as lenses for parallelizing or focusing the light.
Incoherent light sources, however—such as LED chips, for example—have a much more complex radiation characteristic that makes it much more difficult to adapt the optical element.
In conventional lighting devices, therefore, the light source is frequently approximated to a point light source and the optical element is shaped so that the desired radiation characteristic is obtained in combination with a point light source. This approximation is often used for LED chips, in particular, due to the comparatively small dimensions of the chip.
With such lighting devices, however, it can happen that a substantial fraction of the light generated does not exit from the intended decoupling surface, but is instead reflected and ultimately absorbed.
These reflection losses are often compensated for by increasing the radiation power of the light source. However, this typically leads to increased energy consumption and higher thermal stresses on the light source. Modifying the chip design to achieve higher radiation powers, as an alternative in the case of LED chips, usually entails considerable expenditure.